This isn't an answer. How many people I asked, not which people. In any case, I think that your list is haywire:

D300 owners who completly switched to FX (no DX as second equipment)

Why would the buy a 'D400'? Their FX camera already gives them a crop option and most of the speed. No point getting a top end DX as a second camera.

But that's what he meant. Dash at the start denotes "minus", while "+" is, well, a plus :). So IOW he states, that the D300 owners who switched to FF should be subtracted from the total pool of D300 owners, who would want a D400.